CVE-2026-33131
h3 has a middleware bypass with one gadget
Description
H3 is a minimal H(TTP) framework. Versions 2.0.0-0 through 2.0.1-rc.14 contain a Host header spoofing vulnerability in the NodeRequestUrl (which extends FastURL) which allows middleware bypass. When event.url, event.url.hostname, or event.url._url is accessed, such as in a logging middleware, the _url getter constructs a URL from untrusted data, including the user-controlled Host header. Because H3's router resolves the route handler before middleware runs, an attacker can supply a crafted Host header (e.g., Host: localhost:3000/abchehe?) to make the middleware path check fail while the route handler still matches, effectively bypassing authentication or authorization middleware. This affects any application built on H3 (including Nitro/Nuxt) that accesses event.url properties in middleware guarding sensitive routes. The issue requires an immediate fix to prevent FastURL.href from being constructed with unsanitized, attacker-controlled input. Version 2.0.1-rc.15 contains a patch for this issue.
INFO
Published Date :
March 20, 2026, 11:18 a.m.
Last Modified :
March 20, 2026, 1:37 p.m.
Remotely Exploit :
Yes !
Source :
[email protected]
CVSS Scores
| Score | Version | Severity | Vector | Exploitability Score | Impact Score | Source |
|---|---|---|---|---|---|---|
| CVSS 3.1 | HIGH | [email protected] |
Solution
- Update H3 to version 2.0.1-rc.15 or newer.
- Ensure applications use the patched version.
- Review and sanitize Host header input.
- Validate all middleware bypass scenarios.
References to Advisories, Solutions, and Tools
Here, you will find a curated list of external links that provide in-depth
information, practical solutions, and valuable tools related to
CVE-2026-33131.
| URL | Resource |
|---|---|
| https://github.com/h3js/h3/security/advisories/GHSA-3vj8-jmxq-cgj5 |
CWE - Common Weakness Enumeration
While CVE identifies
specific instances of vulnerabilities, CWE categorizes the common flaws or
weaknesses that can lead to vulnerabilities. CVE-2026-33131 is
associated with the following CWEs:
Common Attack Pattern Enumeration and Classification (CAPEC)
Common Attack Pattern Enumeration and Classification
(CAPEC)
stores attack patterns, which are descriptions of the common attributes and
approaches employed by adversaries to exploit the CVE-2026-33131
weaknesses.
We scan GitHub repositories to detect new proof-of-concept exploits. Following list is a collection of public exploits and proof-of-concepts, which have been published on GitHub (sorted by the most recently updated).
Results are limited to the first 15 repositories due to potential performance issues.
The following list is the news that have been mention
CVE-2026-33131 vulnerability anywhere in the article.
The following table lists the changes that have been made to the
CVE-2026-33131 vulnerability over time.
Vulnerability history details can be useful for understanding the evolution of a vulnerability, and for identifying the most recent changes that may impact the vulnerability's severity, exploitability, or other characteristics.
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New CVE Received by [email protected]
Mar. 20, 2026
Action Type Old Value New Value Added Description H3 is a minimal H(TTP) framework. Versions 2.0.0-0 through 2.0.1-rc.14 contain a Host header spoofing vulnerability in the NodeRequestUrl (which extends FastURL) which allows middleware bypass. When event.url, event.url.hostname, or event.url._url is accessed, such as in a logging middleware, the _url getter constructs a URL from untrusted data, including the user-controlled Host header. Because H3's router resolves the route handler before middleware runs, an attacker can supply a crafted Host header (e.g., Host: localhost:3000/abchehe?) to make the middleware path check fail while the route handler still matches, effectively bypassing authentication or authorization middleware. This affects any application built on H3 (including Nitro/Nuxt) that accesses event.url properties in middleware guarding sensitive routes. The issue requires an immediate fix to prevent FastURL.href from being constructed with unsanitized, attacker-controlled input. Version 2.0.1-rc.15 contains a patch for this issue. Added CVSS V3.1 AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N Added CWE CWE-290 Added Reference https://github.com/h3js/h3/security/advisories/GHSA-3vj8-jmxq-cgj5